This invention relates generally to digital VSB (vestigial side band) television receivers and specifically to a simple low cost system for coupling a digital VSB signal from any of a plurality of sources of digital signal (such as an MPEGxe2x80x94Motion Picture Experts Groupxe2x80x94digital signal) to a digital VSB television receiver. While the description is directed to a VSB digital format, it should be understood that the invention in its broader aspects is not limited to a particular digital format.
The recently adopted Digital Television Standard specifies a VSB subsystem having a terrestrial broadcast mode (8 VSB) and a high data rate mode (16 VSB). There are other VSB modes available, namely 2 VSB, 4 VSB and 8 VSB (non terrestrial). The 8 VSB terrestrial mode has the data carrying capability of 4 VSB. (The Trellis coding that is added for the terrestrial environment creates the additional modulation levels.) The digital data signal for video is MPEG encoded and for audio is Dolby AC-3 processed and must be subjected to decompression before application to conventional video and audio circuitry. For terrestrial broadcasting, the data signal is: randomized; subjected to Reed-Solomon (R/S) type encoding for error correction; interleaved; Trellis encoded; multiplexed with segment sync and field sync; supplied with a DC pilot; subject to pre-equalization filtering; modulated; and RF upconverted for transmission. The digital television receiver includes a tuner and a VSB demodulator for developing the baseband signal, which is in compressed form. The demodulated signal is applied to an equalizer for equalizing the received signal. The baseband signal is applied to a transport demultiplexer which directs the data to an appropriate MPEG decoder and a Dolby decoder for recovering the video and audio in proper form for application to video and audio processing circuitry. Digital signals from other sources, such as DVD (digital video disk) players, VCR""s (video cassette recorders), PC""s (personal computers), digital cable boxes, satellite receivers and the like will be supplied to digital television receivers, as is the case for present analog television receivers.
In an analog system, it is well known that coupling the signal from a VCR or other video source to a baseband input of a television receiver (if one is available) yields results superior to those achieved by modulating the signal to RF channel 3 or channel 4 and supplying it to the tuner input of the television receiver. This is not, however, necessarily true in a digital environment in which case the distance between the baseband signal source and the television receiver must be kept relatively short. In an analog system, it is also well known to supply double sideband signals to a receiver.
In accordance with the invention, a compressed baseband digital signal is encoded in a given format for digital transmission and is modulated on an RF carrier for direct application via a cable network or wireless link to the RF input of a digital television receiver. The RF signal, which is at a low power level and has a less-than-nominal bandpass, takes advantage of the front end signal processing that is built into the digital television receiver. Signal impairments, due to the less-than-nominal bandpass characteristic and noise introduced during transmission, that are below a given threshold are corrected by the correction circuitry in the digital television receiver front end. The low signal power, the corrective circuitry for the digital signal and the benign environment of the communications link, enable components and circuits of much lower tolerance (and cost) to be used in the encoding and modulating process. The result is an encoder-modulator that is very low cost and very effective in coupling a digital baseband signal to a digital television receiver over an RF channel.
A principal object of the invention is to provide a novel digital signal translation system.
Another object of the invention is to provide a digital encoder-modulator for coupling a baseband digital signal to a VSB digital television receiver.
A further object of the invention is to provide a low cost digital signal coupling system for a VSB digital television receiver.